The present invention relates, in general, to semiconductor transistors, and more particularly, to heterostructure transistors.
Heterostructure insulated gate field effect transistors (HIGFET's) are well known to those skilled in the art and are widely used for a variety of applications including complementary digital circuits. These prior HIGFET's generally are formed by growing a high mobility channel layer on a gallium arsenide substrate, followed by an aluminum gallium arsenide insulator covering the channel layer. A refractory metal gate is applied on the portion of the insulator. Other portions of the insulator extend over other portions of the transistor including source and drain areas, and generally covers the entire transistor.
One problem with these prior HIGFET's is the high gate leakage current. In complementary circuits, this high leakage current increases the standby power dissipation.
Also, N-type HIGFET's have a turn-on voltage, typically about 1.5 volts, that is lower than P-type HIGFET's, generally about 1.8 volts. This low turn-on voltage also results in high standby power dissipation.
Accordingly, it is desirable to have HIGFETs that have a low gate leakage current.